1. Field of the Invention
The present invention relates to a semiconductor device including a vertical transistor and a horizontal transistor. The present invention also relates to a method of manufacturing the semiconductor device.
2. Description of the Related Art
US 2008/0135932 A (corresponding to JP-A-2008-166705) discloses a semiconductor device in which a semiconductor substrate is divided into a plurality of field areas by a plurality of isolation trenches. In at least one of the field areas, a double-sided electrode element having electrodes on both sides of the semiconductor substrate is formed. In at least another one of the field areas, a single-sided electrode element having a pair of electrodes on one side of the semiconductor substrate is formed. The double-sided electrode element includes a vertical transistor in which electric current flows in a thickness direction of the semiconductor substrate. The single-sided electrode element includes a horizontal transistor in which electric current flows in a direction perpendicular to the thickness direction of the semiconductor substrate, that is, in a direction along a surface of the semiconductor substrate.
In the semiconductor device, electrodes of a plurality of vertical transistors formed on one side of the semiconductor substrate are electrically coupled with each other through a wire, and electrodes of the vertical transistors formed on the other side of the semiconductor substrate are electrically coupled with each other through a wire for forming a circuit by the vertical transistors (see FIG. 6B in US 2008/0135932 A). The circuit can be electrically coupled with an external device by bonding outer wires to pads which are coupled with the wires. In a portion of the semiconductor substrate adjacent to the one side, PN junction parts of the vertical transistors and the horizontal transistors are disposed. Thus, stress during bonding the outer wires may be applied to the PN junction parts, and electric properties of the transistors may change.
For restricting, such a failure, a lead may be coupled with the wires through a die bonding material. However, in this case, the lead needs to be processed so as to correspond to the pads of the wires which are arranged to form the circuit. Thus, the lead is divided and a heat radiation performance of the lead may be reduced. Especially in a case where the vertical transistors form a power section for electric power and the horizontal transistors form a control section for driving the power section, if the heat radiation performance is reduced, heat generated at the power section may be transmitted to the control section, and the control section may malfunction.